Photographic emulsion stabilized with bis (p-acylamidophenyl) disulfides



United States assignors to Eastman Kodak Company, Rochester, N.Y., 5

a corporation of New Jersey No Drawing. Filed Dec. 29, 1964, Ser. No.421,994 14 Claims. (Cl. 96109) ABSTRACT OF THE DISCLOSURE Thestabilization against fog of photographic silver halide emulsions usingbis(p-acylamidophenyl)disulfides is disclosed.

This invention relates to stabilized photographic compositions. Moreparticularly, this invention relates to the stabilization ofphotographic silver halide emulsions. In a specific aspect, thisinvention relates to inhibiting development of spontaneous fog withoutadversely affecting the sensitivity of a photographic silver halideemulsion.

It is known that photographic silver halide emulsions on storage tend tolose sensitivity and to become spontaneously developable withoutexposure to light. There is normally a detectable amount of the silversalt reduced during development in the area where no exposure was given;this is commonly called fog and sometimes called chemical fog where itis necessary to distinguish between it and the effects of accidentalexposure to radia tion.

Certain organic disulfides have been described as being effective inpreventing an increase in fog and to stabilize or control the keepingquality of photographic emulsions. However, many of these organicdisulfides are not elTective antifoggants unless they are used incombination with other materials and still others cause objectionabledesensitization of the emulsion. For example, US. Patent 2,440,110discloses that organic disulfides such as diphenyl disulfide or ditolyldisulfide must be used in combination with sulfinic or seleninic acidsor their salts to obtain acceptable stabilization. It is evident,therefore, that the state of the art will be enhanced by providingphotographic silver halide emulsions which are stabilized by organicdisulfides which are not subject to the aforementioned deficiencies.

Accordingly, it is an object of this invention to provide stabilizedphotographic silver halide emulsions.

Another object of this invention is to provide a method for stabilizingphotographic silver halide emulsions.

Another object of this invention is to provide a method of stabilizingphotographic silver halide emulsions without adversely affecting, to anysubstantial extent, the sensitivity of the emulsion.

Still another object of this invention is to provide photographic silverhalide emulsions which are stabilized with organic disulfides.

Other objects will become apparent from an examination and considerationof the specification and claims that follow.

In accordance with this invention, it has been found that photographicsilver halide emulsions can be stabilized and the development ofspontaneous fog substantially inhibited by the use of at least onebis(p-acylamidophenyl) disulfide having the formula:

where each R is a trifluoromethyl, alkyl or aryl radical. In view of theteachings of US. Patent 2,440,110, it

could not have been predicted that the substituted phenyl disulfidesemployed in the practice of this invention would be effectivestabilizers for photographic silver halide emulsions and prevent thedevelopment of spontaneous fog. Thus, US. Patent 2,440,110 indicatesthat structurally closely related organic disulfides, i.e., aryldisulfides having unsubstituted aromatic rings and aromatic ringscontaining such substituents as carboxylic acid, primary amino or alkylgroups, do not exhibit antifoggant activity. Furthermore, as shown byExample 4, set out hereinafter, other seemingly slight changes in thechemical structure of the disulfide have significant deleterious effectsupon the speed, stability and/or development of spontaneous fog ofphotographic silver halide emulsions containing such disulfide.

As already indicated, the stabilizers employed in the practice of thisinvention have the formula:

I t l where each R is a trifluoromethyl, alkyl or aryl radical. It isobvious that the 0 all group is an acyl radical derived from analiphatic or aromatic carboxylic acid. The R groups, except in the caseof trifluoromethyl, are hydrocarbon and generally contain up to about20, preferably up to 10, carbon atoms. The preferred alkyl groupscontain 1-10 carbon atoms. Suitable R groups include, for example,trifluoromethyl, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,octyl, decyl, dodecyl, eicosyl, phenyl, tolyl, naphthyl, anthryl, andthe like. Hence, examples of the disulfide employed in the practice ofthis invention include bis(p-acetamidophenyl)disulfide,

bis (ptrifluoroacetarnidophenyl disulfide, bis (p-butyramidophenyl)disulfide,

bis (p-propionamidophenyl) disulfide,

bis (p-octanamidophenyl) -disulfide, bis(p-decanamidophenyl)disulfide,

bis (p-pentadecanamidophenyl) disulfide, bis (p-benzamidophenyl)disulfide,

bis p-naphthamidophenyl) disulfide and the like.

A convenient method for preparing the bis(p-acylamidophenyl)disulfidestabilizers employed in practicing this invention comprises reacting4,4'-diamidodiphenyl disulfide with the appropriate carboxylic acidanhydride as represented by the following equation:

R-ii-iI-O-s-swhere each R is as defined hereinbefore. The reactiongenerally takes place at relatively mild temperatures, for example,temperatures up to about C. Normal atmospheric pressures are preferablyemployed although pressures substantially below or above normalatmospheric pressures can be used. If desired, the reaction can becarried out in an inert organic vehicle, and will go to completion in arelatively short period, generally not more than about 4 hours. Theresulting bis(p-acylamidophenyl)disulfides can then be isolated byconventional procedures, for example, filtering, Washing and drying. Thesynthesis of bis(p-acetamidophenyl)disulfide by this procedure is shownin Berichte 38, p. 1134 (1905) and lEI O Nil-R 1120 2RCOOH 3 BeilsteinOrgan. Chem, vol. XIII, p. 544 (1930). As is obvious to those skilled inthe art, other bis(p-acylamidophenyl) disulfides used in practicing thisinvention can be prepared in the same manner by employing theappropriate carboxylic acid derivative in the reaction.

The stabilizing concentration of the bis(p-acylamidophenyl)disulfideemployed in a given emulsion is subject to wide variation, dependingupon the effects desired, degree of ripening, silver content of theemulsion, etc. In general, a concentration in the range of about .001 toabout 10, preferably about .1 to about 1 gram per mole of silver halideis adequate. The stabilizer can be incorporated directly into the silverhalide emulsion layer or it can be present in an adjacent layer. It isgenerally desirable to use higher concentrations of stabilizer when itis used in an adjacent layer rather than in the silver halide emulsionlayer. Exposure of the treated emulsion in conventional photographictesting apparatus such as an intensity scale sensitometer, will revealthe most advantageous concentration for the present stabilizers in aparticular emulsion. Such techniques are well known to those skilled inthe art.

The stabilizers of this invention can be added to the photographiccomposition using any techniques suitable for this purpose. For example,they can be dissolved in a suitable solvent and added directly to thesilver halide emulsion or they can be added to the emulsion in the formof a dispersion similar to the technique used to incorporate certaintypes of color forming compounds (couplers) in a photographic emulsion.The solvent should be selected so that it has no harmful effects uponthe emulsion, in accordance with usual practice, and organic solvents ordiluents are preferred. Examples of suitable solvents or diluentsinclude ethanol, acetone or the like.

The stabilizing addenda employed in the practice of this invention canbe used in various kinds of photographic emulsions. In addition to beinguseful in orthochromatic, panchromatic and infrared emulsions, they arealso useful in X-ray and other non-optically sensitized emulsions. Theycan be added to the emulsions before or after any optically sensitizingdyes which may be used. They are particularly effective in sulfur andgold sensitized silver halide emulsions. Various silver salts can beused as sensitive salts, including, for example, silver bromide, silveriodide, silver chloride or mixed silver halides such as silverchlorobromide, silver bromoiodide or silver chloroiodide. The subjectaddenda can be used in emulsions intended for color photography, forexample, emulsions containing color forming couplers or emulsions to bedeveloped by salts containing couplers or other color generatingmaterials.

In the preparation of the silver halide dispersions employed forpreparing silver halide emulsions there can be employed as thedispersing agent for the silver halide in its preparation, gelatin orsome other colloidal material such as colloidal albumin, a cellulosederivative or a synthetic resin, for example, a polyvinyl compound,although gelatin is preferred.

The photographic emulsions stabilized according to this invention can becoated on a wide variety of supports. Typical supports include thosegenerally employed for photographic elements, as exemplified bycellulose nitrate film, cellulose acetate film, polyvinyl acetal film,polystyrene film, polyethylene terephthalate film and related films ofresinous materials as well as glass, paper, metal, wood and the like.Supports such as paper that are coated with a-olefin polymers,particularly polymers of a-olefins containing 2-10 carbon atoms, as forexample, polyethylene, polypropylene, ethylene butene copolymers and thelike, can also be employed.

In addition to the antifogging addenda, the photographic emulsions andelements can also contain additional additives, particularly those knownto be beneficial in photographic emulsion-s, as exemplified by opticalsensitizers, speed increasing materials, gelatin hardeners, plasticizersand the like.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated.

Example 1 The disulfides disclosed herein stabilize photographicemulsions against increases in fog and decreases in speed even uponstorage at increased temperatures and humidity. To illustrate,bis(p-acetamidophenyl)disulfide is incorporated into a negative, highspeed gelatino silver bromoiodide emulsion containing a yellow dyeforming coupler. The emulsion is coated on a cellulose acetate filmbase. For comparison, three samples of the identical emulsion, onesample containing no antifoggant compound, one containing ditolyldisulfide and one containing diphenyl disulfide are coated on celluloseacetate film base in the same manner. Samples of the preparedphotographic elements are then incubated for 7 days at F. and 50%relative humidity, exposed for second in the form of film strips in anintensity scale sensitometer (Kodak Type Ib) and developed for 12minutes at 75 F. The developer employed has the following formula:

Water to 1.0 liter.

A negative silver image and a yellow dye image is formed. The silverimage and the residual silver halide are removed by treatment with aconventional ferricyanide bleach followed by a hypo fixing bath leavinga yellow negative dye image.

The results of sensitometric tests on the samples are summarized by thedata set out in Table 1 below. In Table 1, as well as in the tablesappearing in the following examples, speeds indicated are a function ofthe exposure necessary to give a density of 0.2 above background fog,the initial control speed being taken as 10.0 in each case; and theconcentrations of addenda, if any,

are indicated as grams of addenda per mole of silver halide.

As can be observed from the above table, thebis(pacylamidophenyl)disulfides of this invention impart substantialstabilizing and antifogging properties to photographic silver halideemulsions. It is also significant to note that the practice of thisinvention does not result in substantial loss in speed with the improvedstability. In contrast, Table 1 illustrates that aryl disulfides havingunsubstituted aromatic rings or aromatic rings containing suchsubstituents as alkyl groups are ineffective to impart stabilizing orantifoggant properties to photographic silver halide emulsions. As shownin US. Patent 2,440,110, such aryl disulfides require the presence ofvarious sulfinic or seleninic acids or salts to exhibit any stabilizingeffects. Such additional additives are, of course, not necessary withthe specific organic disulfides employed in the practice of thisinvention.

Example 2 deleterious afiFect on the stability and/or speed of thephotographic silver halide emulsion. To illustrate, the procedure ofExample 3 is repeated with bis(p-acetamidophenyl)disulfide andbis[o-(N-ethyl)acetamidophenyl] disulfide which has the formula:

The results of sensitometric tests are as follows:

TABLE 4 Concentration After 7 days at 120 F., After 14 days at 120 F.,Addenda of Addenda Initial Test 50% relative humidity 50% relativehumidity (grams/mole of AgX) Speed Fog Speed Fog Speed Fog Control 0 10014 102 21 33 78 Bis(p-acetamidophenyl)disulfide 09 110 09 120 10 78 18 o95 10 112 10 73 18 Bis[o-(N-ethyl)-acetamidophenyl]-disulfide 06 132 12107 18 60 30 D0 40 110 .11 105 .12 62 .18

directly after coating. The results of sensitometric tests are asfollows:

As will be observed from the above table, the bis-[o-(N-ethyl)acetamidophenyl]disulfide, although quite closely Similar resultsare obtained when bis(p-trifiuoroacetamidophenyl disulfide, bis(p-propionamidophenyl disulfide or bis(p-butyramidophenyl)disulfide issubstituted for bis(p-acetamidophenyl)disulfide in the above procedure.

Example 3 related structurally to bis(p-acetamidophenyl)disulfide showsa substantial deleterious effect upon the speed and/ or fog of aphotographic emulsion when it is used in place of the latter. This samedeleterious effect is exhibited by other ortho substituted aryldisulfides such as di-o-formylethylaminodiphenyldisulfide when they areemployed in the above procedure.

Thus, this invention provides silver halide emulsions that arestabilized with antifoggant addenda which do not cause substantialdesensitization or loss in speed.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereinabove and as defined in the appended claims.

TABLE 3 Concentra- After 7 days at tion of Addenda Initial Test 120 F.,rela- Addenda (grams/mole tive humidity of AgX) Speed Fog Speed FogControl 0 100 14 102 20 Bis(p-acetomadophenyl)disulfide. 09 110 09 12010 D0 3 95 10 112 10 As pointed out hereinabove, seemingly slightchanges in the chemical structure of the emulsion addenda employed inthe practice of this invention have a marked We claim: 1. A photographicsilver halide emulsion stabilized with a compound having the formula:

R-ji-EO s s Q-E-E-R where each R is selected from the group consistingof alkyl, trifluoromethyl and aryl.

2. A photographic silver halide emulsion stabilized with about .001 toabout 10 grams per mole of silver halide of a compound having theformula:

Rii M EAR where each R is selected from the group consisting of alkyl,trifluoromethyl and aryl.

3. A photographic silver halide emulsion stabilized with about .1 toabout 1 gram per mole of silver halide of a compound having the formula:

where each R is selected from the group consisting of alkyl,trifluoromethyl and aryl.

4. A photographic silver halide emulsion stabilized with a compoundhaving the formula:

where each R is an alkyl radical containing up to 20 carbon atoms.

5. A photographic silver halide emulsion stabilized with a compoundhaving the formula:

Where each R is an alkyl radical containing 1-10 carbon atoms.

6. A photographic silver halide emulsion stabilized with about .1 toabout 1 gram per mole of silver halide of a compound having the formula:

where each R is an alkyl group containing 1-10 carbon atoms.

7. A photographic silver halide emulsion stabilized with a compoundhaving the formula:

Rif JaQiiA.

where each R is an aryl radical containing up to 20 carbon atoms.

8. A photographic silver halide emulsion stabilized with about .001 toabout 10 grams per mole of silver halide ofbis(p-trifiuoroacetamidophenyl)disulfide.

9. A photographic silver halide emulsion stabilized with about .001 toabout 10 grams per mole of silver halide of his p-acetamidophenyldisulfide.

10. A sulfur and gold sensitized negative, high speed gelatino silverhalide emulsion stabilized with about .001 to about 10 grams per mole ofsilver halide of a compound having the formula:

Where each R is an alkyl radical containing up to 20 carbon atoms.

11. A sulfur and gold sensitized negative, high speed gelatino silverhalide emulsion stabilized with about .001 to about 10 grams per mole ofsilver halide of bis(pacetamidophenyl) disulfide.

12. A high speed gelatin-0 silver bromoiodide emulsion stabilized withabout .25 gram per mole of silver halide ofbis(p-acet-amidophenyl)disulfide.

13. A high speed orthochrornatically sensitized gelatino silverbromoiodide emulsion stabilized with about .25 gram per mole of silverhalide of bis(p-acetamidophenyl) disulfide.

14. A sulfur and gold sensitized negative, high speed gelatino silverbromoiodide emulsion which is stabilized with about .09 gram per mole ofsilver halide of bis(pacetamidophenyl) disulfide.

References Cited UNITED STATES PATENTS 6/1934 Brooker et al. 961097/1956 Ballard 96109

